The invention relates to a bituminous composition comprising a blend of bitumen and a thermoplastic elastomer. More particularly, the invention relates to a bituminous composition comprising a blend of a bitumen such as asphalt and a thermoplastic elastomer containing at least two polymer blocks wherein one of said polymer blocks is a crystalline polymer block having a Tm above 40.degree. C. and one of said polymer blocks is an amorphous polymer block having a Tg of 0.degree. C. or lower.
Bituminous materials especially asphalt have long been utilized in roofing materials particularly in built up roofing (i.e. BUR) application, as road paving materials and as adhesive materials. Unfortunately, however, such materials tend to deteriorate under conditions of extreme temperature variations, constant exposure to physical stress and environmental weathering.
In order to overcome the deficiencies of these bituminous materials particularly asphalt, those active in this field have proposed blending various polymers particularly polyolefins and elastomeric polymers with the asphalt. Thus, polyolefins suchs as polyethylene and polypropylene have been blended with asphalt. However, the polyolefins tend to stiffen the resulting compositions which often results in poor low temperature flexibility. The polyolefin modified asphalts tend to become brittle when exposed to low temperatures and are consequently subject to cracking. Unsaturated elastomers or elastomeric polymers such as polybutadiene and random butadiene-styrene copolymers have been blended with asphalt. However, it has been found that in addition to difficiencies in dimensional stability such unsaturated polymers are susceptible to oxidation particularly when exposed to high temperatures and as a result lose many of their desirable properties such as flexibility and strength.
More recently, those active in the bituminous material field have proposed blending hydrogenated butadiene-styrene random copolymers, butadiene-styrene block copolymers and hydrogenated butadiene-styrene block copolymers with asphalt as shown by the following patents:
U.S. Pat. No. 3,856,732 to Bresson et al., relates to a modified asphalt hydraulic sealer which comprises a cut back asphalt and a small amount (e.g. 1 to 10%) of a butadiene-styrene block copolymer of the SBS type, a hydrogenated random butadiene-styrene copolymer or mixtures thereof or an ethylene-vinyl acetate copolymer.
U.S. Pat. No. 3,978,014 to Van Beem et al., relates to bituminous compositions comprising: (a) 95%-75% by weight of a bituminous component Q having an aromaticity exceeding 0.004+P+0.280 in which P is the N-heptane asphaltene content, (b) 4%-15% by weight of a block copolymer, M.sub.1, preferably a polystyrene-polyalkadiene-polystrene; and (c) 4%-15% by weight of a thermoplastic polymer, M.sub.2, different from M.sub.1 and which has a molecular weight above 10,000, a solubility parameter 7.8-8.8 and a crystallinity below 60% at 25.degree. C. The patent discloses at column 1, lines 46-55 and column 2, lines 48-57 that the block copolymer, M.sub.1 is of the general formula A-B-A in which the A's represent the same or different thermoplastic non-elastomeric polymer blocks prepared by polymerization of one or more monoalkenyl aromatics and in which B represents an elastomeric polymer block prepared either by polymerization of one or more conjugated alkadienes or by copolymerization of one or more conjugated alkadienes with one or more monovinyl aromatics. At column 1, lines 53-55, the patent further discloses that polymer block B may be completely or partly hydrogenated, if desired.
U.S. Pat. No. 4,032,491 to Schoenke relates to a roofing composition for producing a roofing membrane having good bond strength, resistance to cracking, tensile strength and hardness, comprising 5%-40% of asphalt and 60%-95% of a block copolymer of the A-B-A type in which each end block A is formed from a vinyl aromatic monomer and midblock B is a hydrogenated polydiene or a polymer of the ethylene/propylene or ethylene/butylene type. As will be evident, the roofing composition of this patent is basically a block copolymer based composition rather than an asphalt based composition.
U.S. Pat. No. 4,102,849 to Bouton et al., relates to oil-extended hydrogenated diblock copolymers comprising 10-200 parts of oil per 100 parts of a hydrogenated diblock compolymer comprising one block of polybutadiene and one block of a random copolymer of a vinyl arene, such as styrene, and butadiene. The patent, at column 6 lines 53-58, states that the oil-extended hydrogenated diblock copolymers may be utilized for a wide variety of molding operations particularly for rubber hose, shoe soles, tires, industrial and automotive goods, etc. The patent, at column 6 lines 63-68; further discloses that the oil-extended hydrogenated diblock copolymers may be modified by the presence of asphalt, wax, polyvinyl compounds such as polystyrene, ordinary polymers of alpha-olefins such as polypropylene or polyethylene or may be mixed with either natural or synthetic rubbers such as polyisoprene and polybutadiene.
U.S. Pat. No. 4,196,115 to Bresson relates to bituminous or asphalt-based roofing or waterproofing compositions having desirable high and low temperature properties which comprise bitumen or asphalt, at least one radial conjugated diene/monovinyl aromatic copolymer having a weight average molecular weight (Mw) of above 200,000 and a conjugated diene/monovinyl aromatic ratio of 50/50 to 85/15 and at least another or second type radial or linear conjugated diene/monovinyl aromatic copolymer having an Mw of below 200,000 and having the same ratios of conjugated diene/vinyl aromatic. As disclosed in the patent, the conjugated diene/vinyl aromatic copolymers are block copolymers represented by the formula (A-B-A).sub.x Y or (A-B).sub.x Y wherein A represents a non-elastomeric poly(monovinyl aromatic) block containing 8-18 carbon atoms per molecule, and B represents an elastomeric poly (conjugated diene) block containing 4-12 carbon atoms per molecule, Y is at least one atom derived from a polyfunctional treating agent and x represents the number of functional groups of said polyfunctional treating agent and is an integer equal to at least 3.
U.S. Pat. No. 4,282,127, to Desgouilles, relates to a bitumen--based composition comprising a ternary mixture of (a) 52-78 weight % of bitumen, (b) 20-40 weight % polyolefin and (c) 2-8 weight % of a butadiene-styrene copolymer. As set forth in the patent, the butadiene-styrene copolymer may be a random copolymer or a block copolymer with triblock styrene-butadiene-styrene copolymers being particularly suitable.
U.S. Pat. No. 4,610,902 to Eastman et al., relates to a laminate composition useful as a roofing membrane comprising a top and a bottom layer of plastic film bonded together by a modified bitumen material, the top layer of said laminate either containing or being surface coated with an ultraviolet light resistant and absorbing agent. As set forth in the patent, the modified bitumen material is formed by blending a thermoplastic elastomer or thermoplastic rubber or a polyurethane into the bitumen. Thermoplastic elastomers or thermoplastic rubbers disclosed in the patent are styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS) and styrene-ethylene-butylene-styrene (SEBS) block copolymers.
It should be noted that U.S. Pat. No. 4,032,491 and 4,102,849 above appear to be block copolymer based compositions rather than bitumen--or asphalt--based compositions.
Bituminous compositions which have been modified with block copolymers of the SBS type as described in several of the aforementioned patents exhibit a number of advantageous properties particularly good low temperature properties and good dimensional stability. However, such compositions exhibit the significant disadvantage that the unsaturated block copolymers are also susceptible to oxidation when exposed to high temperatures.
Bituminous compositions which have been modified with hydrogenated random copolymers of butadiene-styrene and hydrogenated SBS block copolymers as described in several of the above patents, exhibit a number of advantageous properties including good low temperature and high temperature properties as well as good dimensional stability. However, such compositions also have certain disadvantages. Thus, such compositions are generally difficient in solvent resistance. Moreover, bituminous compositions modified with hydrogenated SBS block copolymers often vary in properties depending upon the nature and type of bitumen which is blended with the hydrogenated SBS block copolymer.
Accordingly, there remains a need for bituminous compositions for roofing application which provide a combination of desirable properties including good low temperature and high temperature properties, weathering resistance, dimensional stability, solvent resistance and uniformity of properties.